Robots may be utilized for a variety of purposes and activities. In a manufacturing and fabrication environment, some robots are utilized to pick up and carry plies of material to a mandrel for shaping. These robots may include an end effector that picks up a ply and applies force to the ply in order to conform the ply with the mandrel.
For example, in an environment where Carbon Fiber Reinforced Polymer (CFRP) is being fabricated, a robot may use an end effector to pick up the ply and place it onto a mandrel defining a surface for the ply. This operation may be performed multiple times for multiple plies in order to build up a composite pre-form of dry carbon fiber. The composite pre-form may then be impregnated with curable resin, and cured in order to form CFRP. During the layup process in which plies are placed onto the mandrel, it remains desirable to prevent the formation of wrinkles within any ply, as wrinkles are not desirable in any fabricated CFRP. Furthermore, as plies of dry carbon fiber are delicate, it also remains important to ensure that the end effector does not apply forces that would undesirably alter a shape of the ply during transport and placement.
This problem is magnified when robots are utilized to transport limp plies. An example of such material is made from rows of unidirectional carbon fiber that have been stitched together. Each row of unidirectional carbon fiber is rigid along its length, but the stitches holding the rows to each other are less rigid than the rows themselves. Since stitches that unite the rows have less rigidity than the rows themselves, each row will hang limp from the other rows if not independently supported. This presents a problem when transporting plies for placement onto a mandrel, because any portion of a ply than hangs limp may fold underneath other portions of the ply when the ply is being placed onto the mandrel, resulting in multiple overlapping layers where only one layer is desired. The overlap causes the ply to fundamentally diverge from the desired final shape defined by the mandrel. The folding of hanging sections of plies also generates multiple wrinkles, bends, and/or warps, all of which are undesirable and may render the ply unusable after shaping on the mandrel.
Hence, fabricators of CFRP continue to seek out end effector technologies that are both capable and cost-effective, particularly in regard to materials which are limp and incapable of supporting their own weight. Therefore, it would be desirable to have a method and apparatus that take into account at least some of the issues discussed above, as well as other possible issues.